In an ink-jet printing system, a liquid ink is ejected from a nozzle towards a printing medium using a pressure, heat or an electric field as a driving source to print the printing medium. The ink-jet printing system can be used with a low running cost and form high quality images. Accordingly, in these years, the ink-jet printing system has been quickly spreading not only as an office printing system but also domestic printing system.
As inks for ink-jet printing, aqueous dye inks, which comprise water-soluble dyes dissolved in aqueous media, are used since they have high coloring properties and cause less clogging of printer head orifices. However, the aqueous dye inks have some drawbacks such as low water-resistance, insufficient durability, etc.
Recently, large-size ink-jet printers, which can accommodate to the A-0 size sheet, have been developed and increasingly used outdoor applications for printing exterior posters. In addition, with the popularization of digital cameras, the ink-jet printing is used in applications where printed materials are stored for a long time. Under such circumstances, pigmented inks with good water resistance and weather resistance are being vigorously developed.
However, the aqueous pigment inks comprising water or an aqueous medium as a solvent are not suitable for printing posters since plain paper sheets are cockled (i.e. waving after drying) when they are printed with such aqueous pigment inks.
Oil-based pigmented inks comprising aliphatic hydrocarbons or alcohols as solvents (for example, inks disclosed in JP-A-2000-38533, JP-A-2001-220527 and JP-A-2001-329193) cause less cockling. However, when they are printed on a cationically treated printing media (in general, gloss paper sheets), printed records tend to be grazed. For example, if a number of sheets are continuously printed, the printed records are easily grazed, when the second and subsequent printed sheets are laminated on the previous sheet for several seconds, or the printed records are touched with a hand after printing.